Wind as a source of energy is a concept that has been promoted for some time. According to one source, there is evidence which shows that windmills were in use in Babylon and in China as early as 2000 B.C. The U.S. Patent and Trademark Office has granted patents on windmill devices dating back to the early to mid 1800's.
Generally, in the art, wind turbines have either a vertical or horizontal axis. Typically, most or all of commercial wind turbines today are built with a propeller-type rotor on a horizontal axis (i.e., a horizontal main shaft) in order that they may face directly into a wind. It is generally known that most horizontal axis turbines built today are two or three-bladed, although some have fewer or more blades. The purpose of the rotor is to convert the linear motion of the wind into rotational energy that can be used to drive a generator.
Worldwide interest in renewable energy options, however, has given rise to a significant increase in new wind turbine designs. Some of the most recent models on the market, therefore, are vertical axis wind turbines (“VAWTs”). Vertical-axis wind turbines are typically of a long axis type, allowing large columns of air to be harnessed.
There exist two main types of VAWTs—the Savonius turbine which is a high speed, low torque turbine and the Darrieus turbine, which is a low speed, high torque turbine. Generally, the Darrieus turbine resembles an egg beater, where two vertically oriented blades revolve around a vertical shaft. Generally, the Darrieus models use an airfoil design so that a wind turbine airfoil essentially works in the same way as an airplane wing so that an airfoil has a flat side and a curved side. The result of air passing over the two sides is a force known as “lift.” When an airplane speeds down a runway, air passing on both sides of the airfoil wings, the lift force literally lifts the airplane into the air. This will continue as long as there is forward motion over the airfoil to generate the required lift.